In general, wet processing of photosensitive material is carried out by dipping the material for a predetermined time in a processing solution such as a developing solution, a bleach-fix solution, and washing water in a processing tank.
The state-of-the-art for the continuous processing of photosensitive material in such a processing bath has a problem that the processing solution evaporates, lowers its temperature or undergoes deterioration or other various changes through oxidation or the like because its surface is open to the ambient atmosphere. As the processing solution evaporates, a difference arises in concentration between the solution near the surface and the solution near the tank bottom, which is undesirable for even development. An extra amount of processing solution or diluent must be fed to make up for such an additional loss of processing solution in the tank. In addition, evaporated processing solution will undesirably deposit on various parts of the processing apparatus, particularly on feed rollers for carrying photosensitive material. Such deposits later dry to present a tacky surface or cause staining. It is apparent that changes of properties or deterioration of processing solution adversely affects development. Further the developing solution, for example, must be maintained at a temperature of about 20.degree. to 50.degree. C. in order to ensure proper development. If a noticeable amount of heat dissipates from the solution surface, an excess amount of heat must be applied to maintain the solution at the optimum temperature.
One solution to prevent evaporation of processing solution is a lid provided in the processing tank near the solution surface to cover the solution surface. However, if the solution surface is entirely covered with the lid, the lid must be removed whenever photosensitive material is carried into the processing tank. Such removal of the lid for every operation is cumbersome. It might occur to the skilled artisan to provide the lid with an opening through which photosensitive material can be carried into the processing tank. Since a part of the lid is always open independent of whether or not the tank is in operation, the processing solution still undergoes evaporation, temperature lowering, deterioration and property changes to some extent, though to a less extent than in the lidless tank.
A variety of processing apparatus are used in such wet processing of photosensitive material. The above-mentioned problems of processing solution including deterioration with time are rather less serious in automatic developing machines for commercial service among others because a large quantity of photosensitive material is daily processed and a corresponding large quantity of processing solution is replenished so that the processing solution in the tank is replaced over relatively a few cycles.
As opposed to such business use machines, wet color copying machines for consumers use, which have marked a rapid advance in these years, expect occasional operation or low utilization. The occasional operation or low utilization operation used herein means that the processor is operated at a few frequency or for a short time as exemplified by an operating efficiency of up to 1/10 round a day (one round represents the amount of film processed until the amount of replenisher added reaches the same as the processing solution originally in the tank) or up to 10% of the process temperature time as described in several manuals, for example, "Fuji Film Processing Manual, CR-56 Processing 163AL004B, General 12/87-KW05-2(1)," pages 73-74 and "Kodak R-3/R-3000 Chemicals CAT 123/5753" (1985), pages 41-42.
The apparatus of this type is generally designed such that a small quantity of processing solution is replenished for every operation. For example, 23 c.c. of developing solution is made up on processing of an A4-size sheet of photosensitive material. In such occasional operation, it takes a long time until the entire quantity of processing solution in the tank is replaced by a fresh solution or replenisher. Then the processing solution in the tank is deleteriously affected by aging.
In consideration of processing solution aging, it is conceivable to periodically replace the processing solution in the tank independent of the quantity of photosensitive material processed thus far. This idea is unacceptable for consumer use processing apparatus because the user has to perform cumbersome operation of replacing processing solution. In addition, the quantity of processing solution consumed is undesirably increased.
It is also conceivable to make up a somewhat excess amount of replenisher to compensate for deterioration of the processing solution. The replenishing amount must be precisely adjusted because an excess or short amount will more or less affect photographic performance. Such fine adjustment is difficult for ordinary users. Further, not only the quantity of replenishing solution used is increased, but the frequency of cumbersome replenishment operation is also increased.